/*
  Copyright (C) 2003-2005 Brian Harring

  This program is free software; you can redistribute it and/or
  modify it under the terms of the GNU General Public License
  as published by the Free Software Foundation; either version 2
  of the License, or (at your option) any later version.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, US 
*/
#include <stdlib.h>
#include <math.h>
#include <diffball/defs.h>
#include <diffball/primes.h>

#define sqr(x) ((x) * (x))

int
init_primes(PRIME_CTX *ctx)
{
		/* heh... the first 1,000 primes... */
		unsigned int primes[] = 
{3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97,
101,103,107,109,113,127,131,137,139,149,151,157,163,167,173,179,181,191,193,197,
199,211,223,227,229,233,239,241,251,257,263,269,271,277,281,283,293,307,311,313,
317,331,337,347,349,353,359,367,373,379,383,389,397,401,409,419,421,431,433,439,
443,449,457,461,463,467,479,487,491,499,503,509,521,523,541,547,557,563,569,571,
577,587,593,599,601,607,613,617,619,631,641,643,647,653,659,661,673,677,683,691,
701,709,719,727,733,739,743,751,757,761,769,773,787,797,809,811,821,823,827,829,
839,853,857,859,863,877,881,883,887,907,911,919,929,937,941,947,953,967,971,977,
983,991,997,1009,1013,1019,1021,1031,1033,1039,1049,1051,1061,1063,1069,1087,1091,
1093,1097,1103,1109,1117,1123,1129,1151,1153,1163,1171,1181,1187,1193,1201,1213,
1217,1223,1229,1231,1237,1249,1259,1277,1279,1283,1289,1291,1297,1301,1303,1307,
1319,1321,1327,1361,1367,1373,1381,1399,1409,1423,1427,1429,1433,1439,1447,1451,
1453,1459,1471,1481,1483,1487,1489,1493,1499,1511,1523,1531,1543,1549,1553,1559,
1567,1571,1579,1583,1597,1601,1607,1609,1613,1619,1621,1627,1637,1657,1663,1667,
1669,1693,1697,1699,1709,1721,1723,1733,1741,1747,1753,1759,1777,1783,1787,1789,
1801,1811,1823,1831,1847,1861,1867,1871,1873,1877,1879,1889,1901,1907,1913,1931,
1933,1949,1951,1973,1979,1987,1993,1997,1999,2003,2011,2017,2027,2029,2039,2053,
2063,2069,2081,2083,2087,2089,2099,2111,2113,2129,2131,2137,2141,2143,2153,2161,
2179,2203,2207,2213,2221,2237,2239,2243,2251,2267,2269,2273,2281,2287,2293,2297,
2309,2311,2333,2339,2341,2347,2351,2357,2371,2377,2381,2383,2389,2393,2399,2411,
2417,2423,2437,2441,2447,2459,2467,2473,2477,2503,2521,2531,2539,2543,2549,2551,
2557,2579,2591,2593,2609,2617,2621,2633,2647,2657,2659,2663,2671,2677,2683,2687,
2689,2693,2699,2707,2711,2713,2719,2729,2731,2741,2749,2753,2767,2777,2789,2791,
2797,2801,2803,2819,2833,2837,2843,2851,2857,2861,2879,2887,2897,2903,2909,2917,
2927,2939,2953,2957,2963,2969,2971,2999,3001,3011,3019,3023,3037,3041,3049,3061,
3067,3079,3083,3089,3109,3119,3121,3137,3163,3167,3169,3181,3187,3191,3203,3209,
3217,3221,3229,3251,3253,3257,3259,3271,3299,3301,3307,3313,3319,3323,3329,3331,
3343,3347,3359,3361,3371,3373,3389,3391,3407,3413,3433,3449,3457,3461,3463,3467,
3469,3491,3499,3511,3517,3527,3529,3533,3539,3541,3547,3557,3559,3571,3581,3583,
3593,3607,3613,3617,3623,3631,3637,3643,3659,3671,3673,3677,3691,3697,3701,3709,
3719,3727,3733,3739,3761,3767,3769,3779,3793,3797,3803,3821,3823,3833,3847,3851,
3853,3863,3877,3881,3889,3907,3911,3917,3919,3923,3929,3931,3943,3947,3967,3989,
4001,4003,4007,4013,4019,4021,4027,4049,4051,4057,4073,4079,4091,4093,4099,4111,
4127,4129,4133,4139,4153,4157,4159,4177,4201,4211,4217,4219,4229,4231,4241,4243,
4253,4259,4261,4271,4273,4283,4289,4297,4327,4337,4339,4349,4357,4363,4373,4391,
4397,4409,4421,4423,4441,4447,4451,4457,4463,4481,4483,4493,4507,4513,4517,4519,
4523,4547,4549,4561,4567,4583,4591,4597,4603,4621,4637,4639,4643,4649,4651,4657,
4663,4673,4679,4691,4703,4721,4723,4729,4733,4751,4759,4783,4787,4789,4793,4799,
4801,4813,4817,4831,4861,4871,4877,4889,4903,4909,4919,4931,4933,4937,4943,4951,
4957,4967,4969,4973,4987,4993,4999,5003,5009,5011,5021,5023,5039,5051,5059,5077,
5081,5087,5099,5101,5107,5113,5119,5147,5153,5167,5171,5179,5189,5197,5209,5227,
5231,5233,5237,5261,5273,5279,5281,5297,5303,5309,5323,5333,5347,5351,5381,5387,
5393,5399,5407,5413,5417,5419,5431,5437,5441,5443,5449,5471,5477,5479,5483,5501,
5503,5507,5519,5521,5527,5531,5557,5563,5569,5573,5581,5591,5623,5639,5641,5647,
5651,5653,5657,5659,5669,5683,5689,5693,5701,5711,5717,5737,5741,5743,5749,5779,
5783,5791,5801,5807,5813,5821,5827,5839,5843,5849,5851,5857,5861,5867,5869,5879,
5881,5897,5903,5923,5927,5939,5953,5981,5987,6007,6011,6029,6037,6043,6047,6053,
6067,6073,6079,6089,6091,6101,6113,6121,6131,6133,6143,6151,6163,6173,6197,6199,
6203,6211,6217,6221,6229,6247,6257,6263,6269,6271,6277,6287,6299,6301,6311,6317,
6323,6329,6337,6343,6353,6359,6361,6367,6373,6379,6389,6397,6421,6427,6449,6451,
6469,6473,6481,6491,6521,6529,6547,6551,6553,6563,6569,6571,6577,6581,6599,6607,
6619,6637,6653,6659,6661,6673,6679,6689,6691,6701,6703,6709,6719,6733,6737,6761,
6763,6779,6781,6791,6793,6803,6823,6827,6829,6833,6841,6857,6863,6869,6871,6883,
6899,6907,6911,6917,6947,6949,6959,6961,6967,6971,6977,6983,6991,6997,7001,7013,
7019,7027,7039,7043,7057,7069,7079,7103,7109,7121,7127,7129,7151,7159,7177,7187,
7193,7207,7211,7213,7219,7229,7237,7243,7247,7253,7283,7297,7307,7309,7321,7331,
7333,7349,7351,7369,7393,7411,7417,7433,7451,7457,7459,7477,7481,7487,7489,7499,
7507,7517,7523,7529,7537,7541,7547,7549,7559,7561,7573,7577,7583,7589,7591,7603,
7607,7621,7639,7643,7649,7669,7673,7681,7687,7691,7699,7703,7717,7723,7727,7741,
7753,7757,7759,7789,7793,7817,7823,7829,7841,7853,7867,7873,7877,7879,7883,7901,
7907,7919,7933};

	unsigned int x;
	if((ctx->base_primes = (unsigned int *)malloc(1000 * sizeof(int)))==NULL) {
		return MEM_ERROR;
	}
	ctx->prime_count=1000;
	ctx->array_size = 1000;
	for(x=0; x < ctx->prime_count; x++)
		ctx->base_primes[x] = primes[x];
	return 0L;
}

void 
free_primes(PRIME_CTX *ctx)
{
	free(ctx->base_primes);
	ctx->prime_count = ctx->array_size = 0;
}

int
find_next_prime(PRIME_CTX *ctx)
{
	unsigned long prime, upper, x;
	int is_prime=0;
	if(ctx->prime_count == ctx->array_size) {
		ctx->array_size += 1000;
		if((ctx->base_primes=(unsigned int *)realloc(ctx->base_primes,
			(ctx->array_size)*sizeof(int)))==NULL) {
			return MEM_ERROR;		
		}
	}
	prime = ctx->base_primes[ctx->prime_count-1] + 2;
	while(! is_prime) {
		upper = ceil(sqrt(prime));
		is_prime=1;
		for(x=0; is_prime && ctx->base_primes[x] <= upper; x++) {
			if(prime % ctx->base_primes[x]==0) {
				is_prime=0;
			}
		}
		if(! is_prime) {
			prime+=2;				
		}
	}
	ctx->base_primes[ctx->prime_count] = prime;
	ctx->prime_count++;
	return 0L;
}

unsigned long 
get_nearest_prime(unsigned long near)
{
	PRIME_CTX ctx;
	unsigned long x, y, div, prime;
	int is_prime;

	if(init_primes(&ctx))
		return 0;
	prime = 0;
	if(near < ctx.base_primes[ctx.prime_count -1]) {
		x=0;
		while(ctx.base_primes[x] < near) {
			x++;
		}
		if(x==0) {
			prime = ctx.base_primes[x];
		} else if(abs(near - ctx.base_primes[x]) > abs(near - ctx.base_primes[x-1])) {
			prime = ctx.base_primes[x-1];
		} else {
			prime = ctx.base_primes[x];
		}
	}
	if(prime) {
		free_primes(&ctx);
		return prime;
	}
	div=0;
	if(!(near % 2)) {
		near++;
	}
	/* dealing w/ upper limit of unsinged longs. */
	if(near==0xffffffff) {
		near-=2;
	}
	if(sqr(ctx.base_primes[ctx.prime_count -1]) < near) {
		while(sqr(ctx.base_primes[ctx.prime_count -1]) < near && ctx.base_primes[ctx.prime_count -1] != 65521) {
			if(find_next_prime(&ctx)) {
				free_primes(&ctx);
				return 0;
			}
		}
		div = ctx.prime_count -1;
	 } else {
		x=0;
		while(sqr(ctx.base_primes[x]) < near) {
			x++;
		}
		div=x;
	}		
	for(x=0, is_prime=1; x< div && is_prime; x++) {
		if(near % ctx.base_primes[x]==0) {
			is_prime=0;
		}
	}
	if(is_prime) {
		return near;
	}
	y=0;
	prime=0;
	while(prime==0) {
		is_prime=1;
		y+=2;
		/*again, dealing w/ upper limit of unsigned longs. */
		if(near < 0xffffffff -y) {
			for(x=0; x <= div && is_prime; x++) {
				if((near +y) % ctx.base_primes[x]==0) {
					is_prime=0;
				}
			}
			if(is_prime) {
				prime = near +y;
			}
		}
		if(prime==0) {
			is_prime=1;
			for(x=0; x <= div && is_prime; x++) {
				if((near -y) % ctx.base_primes[x]==0) {
					is_prime=0;
				}
			}
			if(is_prime) {
				prime = near -y;
			}
		}
	}
	free_primes(&ctx);
	return prime;
}

